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How long does SARS-CoV-2 persist in people after infection? Kobi Wolf/Bloomberg via Getty Images
  • A new study suggests that the recent trend of shortening isolation and quarantine periods for COVID-19 may be in error.
  • The scientists measured the presence of active virus using RNA sequences rather than virus fragments, which polymerase chain reaction (PCR) testing detects.
  • They found that more than 1 in 10 people who have tested positive for SARS-CoV-2 retained active infections for more than 10 days.
  • It is not clear whether the extended presence of active virus means that it remains infectious.

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As the COVID-19 pandemic continues, health authorities have been revising the amount of time people with a SARS-CoV-2 infection should remain in isolation or quarantine.

The Centers for Disease Control and Prevention (CDC) currently recommend that people who test positive for SARS-CoV-2 should remain in isolation for 5 days, followed by 5 days of wearing a face mask around others. The guidance for quarantine is the same.

A new study finds evidence that 13% of those who have tested positive for a SARS-CoV-2 infection retained active infections for more than 10 days.

The researchers found clinically significant levels of the SARS-CoV-2 virus for as long as 68 days in some individuals.

Of additional concern is that there was nothing clinically remarkable about those whose infections exceeded 10 days, making their identification using symptoms or other external signs difficult or impossible.

The researchers from the University of Exeter in the United Kingdom retroactively examined subgenomic RNA (sgRNA) and E gene genomic sequences in 176 people who had received positive PCR test results.

Lorna Harries, senior author of the study and Exeter’s professor of molecular genetics, explained sgRNA to Medical News Today:

“When [SARS-CoV-2] is actively growing, parts of its RNA sequence that are not usually found close together become joined together. This is sgRNA, an abbreviation for subgenomic RNA. Measuring this allows us to get a measure of whether or not the virus detected could be active and potentially infectious.”

PCR testing tests for SARS-CoV-2 fragments. While their presence confirms that a person has gotten an infection, the test is unable to differentiate between dead and still replicating virus.

Although the authors of the current study believe that sgRNA “provides a marker for actively replicating virus,” not everyone agrees.

“With this study, it is important to recognize that it is unclear whether the presence of sgRNA is indicative of contagiousness,” Johns Hopkins’ Dr. Amesh Ashok Adalja told MNT. Dr. Adalja, an assistant professor, was not involved in the study.

The findings of the study appear in the International Journal of Infectious Diseases.

Periods of isolation or quarantine are disruptive to peoples’ lives and jobs. As a result, health authorities have good reason to keep these interruptions as short as medically possible.

Moreover, the CDC asserts that the evidence supports its new recommendations,

“The change is motivated by science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1–2 days prior to onset of symptoms and the 2–3 days after.”

Dr. Adalja said the new study does not mean that the CDC is making a mistake, because “the goal is to provide guidance that people can actually follow that also blocks the bulk of transmission.”

He noted that there is “long-standing data from case contact investigations illustrating that transmission becomes exceedingly rare 5 days post-symptom onset.”

Prof. Harries did not agree, saying, “I am uneasy about a change to a 5-day isolation, based on our data, as well as that of others.”

“Deciding duration of isolation is obviously a balance between preventing transmission and keeping society open,” Prof. Harries added, “but our data suggest that people will differ in how long they are infectious for, and particularly in vulnerable settings, like care homes for older people, it might be prudent to use additional safeguards to protect people.”

New SARS-CoV-2 variants are also a concern, said Prof. Harries. “Since Delta and Omicron are so much more infectious, the amount of virus that needs to be transferred to infect someone else may well be lower, so more people would fall above a threshold for clinical relevance.”

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